Primary sources are the evidence of history, original records or objects created by participants or observers at the time historical events occurred or even well after events, as in memoirs and oral histories. Primary sources may include but are not limited to: letters, manuscripts, diaries, journals, newspapers, maps, speeches, interviews, documents produced by government agencies, photographs, audio or video recordings, born-digital items (e.g. emails), research data, and objects or artifacts (such as works of art or ancient roads, buildings, tools, and weapons). These sources serve as the raw materials historians use to interpret and analyze the past.
(Definition and image: Primary Sources on the Web: Finding, Evaluating, Using, Reference and User Services Association)
Below are select online archives, but they are extensive in number and scope! Search for online archives by using topic keywords and select words like "archives," "collections," or "exhibits." Look for results hosted by a museum, school, government institution, or other "official" entity. Ask for help if you're not sure, or you can't find something!